1. Field of the Invention
The present invention generally relates to methods for enhancing the response speed of hold-typed display devices, and more particularly to a method increasing the output frame rate in a way to achieve response speed enhancement.
2. The Prior Arts
The liquid crystal display (LCD) devices have been the mainstream display technology in recent years. However, due to the physic property of liquid molecules, LCD devices are significantly inferior to the cathode ray tube (CRT) display devices in terms of response speed. Therefore, this has been the major research and development focus for both industrial and academic arenas.
FIG. 1a is a schematic diagram showing the architecture of a conventional LCD device. As illustrated, the LCD device contains a direct-lit backlight module (denoted as “LED backlight”) using multiple LEDs arranged in a number of horizontal rows (denoted as “BL1,” “BL2,” “BL3,” and so on). Each row of LEDs is driven by a driver which in turn is controlled by a driver control circuit. The backlight module usually contains a diffuser so as to scatter the light beams emitted from the LEDs into uniform planar light. The LCD panel, on the other hand, contains multiple vertically aligned data lines D1, D2, . . . , Dm (only D1 is depicted) and horizontally aligned scan lines G1, G2, . . . , Gn (only G1 is depicted). A pixel of the LCD panel is located at the intersection of a data line and a scan line (e.g., the pixel P1 is located at where D1 and G1 intersect). Each data line is driven by a data driver while each scan line is enabled by a gate driver. The data drivers and gate drivers are controlled by a control board of the LCD device.
The brightness of a pixel (e.g., P1) is determined by the backlight and the gray level of the pixel P1 which is the result of enabling the scan line G1 by a gate driver and then exerting a driving voltage over the data line D1 by a data driver. Under the operation of the driving voltage, the gray level of the pixel P1 gradually approaches, instead of directly becomes a target gray level. Due to such a delay property of the liquid molecules, LCD device is commonly referred to as a hold-typed display device where residuals and therefore blurs in the displayed images are inevitable especially when dynamic images are presented. To solve this problem, various methods for accelerating the response speed of LCD device have been disclosed in the art. FIG. 1b is a timing diagram showing the waveforms of various signals of the LCD device of FIG. 1a. Please note that a technique called column inversion is adopted by the LCD device of FIG. 1 which one of the techniques to periodically reverse the polarity of the driving voltage applied to a liquid molecule without affecting its gray level so that the liquid molecule will not be damaged by a constant driving voltage applied for an extended period of time. In the diagram, the Vsync waveform shows the vertical synchronization signal from of LCD device, G1˜Gn waveforms show the enablement signals of the scan lines G1˜Gn whose pulse width is determined by the horizontal synchronization signal, Hsync, of the LCD device, D1 waveform shows the driving voltage applied to the data line D1, Vlc waveform shows the voltage level of the pixel P1, B1 waveform shows the control signal applied to the backlight module, and P1 waveform shows the variation of the brightness (i.e., gray level) of the pixel P1.
As shown in FIG. 1b, assuming that the pixel P1 has a target gray level corresponding to a voltage level (hereinafter, the target voltage level) code 16 in frame N−1 and the target voltage level code200 in frame N. If the driving voltage code200 is applied to the pixel P1 during the frame N, the gray level of the pixel P1 gradually approaches the target gray level (denoted as “Target”) as shown by the curve marked as “original.” A conventional acceleration technique is to apply an overdriving voltage code220 that is larger than the original voltage level code200. The gray level of the pixel P1 approaches the target gray level in frame N in a faster speed as shown by the curve marked as “overdriving.” Another conventional technique is to apply an overdriving voltage code230 to the pixel P1 in the first half of the time showing frame N (hereinafter, the frame time) and the driving voltage code200 in the second half of the frame time. This approach requires that the frame rate being doubled from the standard 60 Hz to 120 Hz and is therefore referred to as an overdriving method of double frame rate (DFR). In this approach, the gray level of the pixel P1 approaches the target gray level in frame N in an even faster speed as shown by the curve marked as “DFR overdriving.” Please note that, as shown by the curve BL, the backlight is always turned on.
The aforementioned DFR overdriving method has proven to be effective in enhancing the response speed of the LCD device. As shown in FIG. 1c, from the point of view of the control board of the LCD device using the DFR overdriving method, the frames input into the control board in the 60-Hz frame rate are denoted in a timing sequence marked as “Input frames,” and the frames output from the control board in the 120-Hz frame rate are denoted in another timing sequence marked as “Output frames.” During the first half of the frame time of the input frame N+1, for example, the control board outputs the data of the frame N again as data for the frame N+1 is not yet completely received by the control board. Then, in the second half of the frame time of the input frame N+1, the control board is able to output the data of the frame N+1 from the data already collected from the first half of the input frame time and the data concurrently received in the second half of the input frame time. In other words, the DFR overdriving method would output the data of an input frame twice (one using overdriving voltages and one using target driving voltages). This repetition would cause some interruptions for dynamic images but these interruptions are usually so short to notice for human eyes.
Another similar acceleration method also using DFR is to output a completely black frame in the first half of the input frame time of, say, frame N+1, and then to output the data of the frame N+1 using target driving voltages. A variation of the method is to output the completely black frame in the second half of the input frame time of, say, frame N+1. This so-called black-insertion approach has an advantage in achieving a display effect comparable to the impulse-typed display device such as CRT.